Dirsort might help with that, kind of autosort, but for any directory.

For the second question, the problem you'll find with the ST and jpg's is that you probably will have difficulty working with true colour large images on the ST itself. Given the 4mb memory limit you will find you will run out of memory pretty quickly as soon as the ST tries to decompress the image with most conversion programs, plus it will be painfully slow. Unless you have a Falcon, TT or clone, I would leave the image editing to the PC, unless your jpgs are small and colour limited.

You could also try plastic 'welding'. I used it to repair an Atari monitor case. You can do it from inside and then sand down. You need an old soldering iron, super glue and baking soda, as well as some donor plastic, there are plenty of instructional videos on youtube.

Is it a 1mb or 512k upgrade. I notice there are empty memory chip sockets - so presumably 512k upgrade? If it is 1mb though the reason nothing works without it in could be that the internal memory has been disabled (something you would have to do with 1mb to stop the machine having 1.5mb which the ST doesn't support). Check for some snipped components near the motherboard memory. My other thought if that is not the case, is that the mounting over the MMU is to blame. I would check connections there (not pressed in correctly when you reseated it, or the socket pins aren't making good connection. I can't see how that adaptor fits over the mmu, Is it socketed and press in (i.e. pins on the adaptor push into the socket) or press on (i.e. that socket fits over a surface mounted MMU) or is it soldered on? Finally it could be the ram has gone bad, either on the upgrade board or on the motherboard, as it seems socketed on the upgrade you could try replacing that..

As for these ST light gun games, as others have asked, will they work on the ST's RGB monitor or do you have to have an 520STm, an STFM, or an STe to be able to connect a composite monitor or TV to play them with?

From memory I believe I played Space Gun at least on a Phillips monitor, which has the same internals as the Atari one. Any CRT should be fine I think.

Are there any compatibility issues between these versions? My STE has (I thinK) 1.62. I use 206 under emulation and like its additional features. Im trying to determine if I should track down a ROM set for it.

If you can get a switcher, that would be best. TOS 2.06 is far better to work with on a day to day basis, but has issues with quite a few games (particularly early ones). I have 2.06 and 1.02 in my STFM which gives the best of both worlds. I don't often swap back, but if I do need to then it's there if I need it. If you don't play games that much then imo its a no brainer, get 2.06 in there, particularly as it is just a ROM swap.

I would stay away from this type of upgrade as it is very flaky it will make your computer in inoperable

That's a bit harsh, I've had them in several STs for years without any problems at all, overall I would say they are pretty solid if they are installed correctly (and don't want to run any other upgrades like a speed booster)

The only one I had problems with was the fit socket over the soldered MMU type. One literally popped off after some time, killing itself.

The Marpet memory upgrade clips (or should I say squeezes?) over the top of MMU and under the shifter. The shifter is in the silver box in the middle of the ST motherboard (its the largest chip in there). The mmu moves about depending on motherboard revision, but is a square shaped chip (there are two or three in there depending on whether a blitter is installed). If the chip is socketed it will look like just that, a chip in a socket (the shifter mostly is, the mmu not so much), if the chip is soldered directly to the motherboard it will be a pain to add a memory upgrade. Back in those days you would get some extra sockets that would plug into the Marpet that kinda acted like an upside down socket, which would fit over the offending soldered chip. They were a bit crappy though and usually worked loose at the slightest opportunity. You usually had to glue gun them in to keep them from popping off. If the shifter is not socketed, you are buggered, unless you feel comfortable desoldering the chip and fitting a socket and a new chip (or the original if by some miracle you haven't cooked it during the desoldering) or soldering the upgrade directly onto the chip itself. It tends to be the later STFMs that are soldered (cost cutting). If you have TOS 1.04 (unless the system has been upgraded) and a late release date/ motherboard revisiion, you are more at risk of this.

If your chips are socketed, you simply have to orientate the one bit of the upgrade correctly over the mmu then push the pins in between the chip and the socket. This is a little hair raising the first time, and also puts some extra strain on the pins in the socket, which might make the socket a bit unreliable if you ever take the memory out. From memory the other bit for the shifter, you remove the chip, add the thru socket and then reseat the shifter, making sure the orientation is right (or fried chip results). It's not hard after you have done one, but can be little daunting for the first timer. You just need to make sure you check everything a thousand times and read the manual a lot.

I believe Exxos also has some memory upgrades, which are probably going to be a darn sight more reliable than some ancient simms/ memory and a marpet upgrade.

Magic was awesome back then, a combo of it, NVDI and Jinnee brings Mac level useability, with incredible speed (for a 8 - 32mhz cpu platform). Kept me from having to buy a Mac or PC for many years longer

I'd keep the accs and auto programs to the minimum if you can, as the more there are the more there is a chance of conflict. In these days of endless storage I stopped using a boot manager and instead hand crafted different (auto) folders containing different sets of programs for the various circumstances, I then just rename the folder auto and reboot. For example I have a basic folder which just has some of the basic essential patches like folder xxx and so on, for booting in plain TOS. I then have a GDOS folder for programs like Timeworks that really only get on with clunky old GDOS. And a 'power' (ha ha) user folder with NVDI, Magic and all the trimmings (and 2mb of ram gone like that!). Managing the autofolder is a bit of a dark art... the key rule is 'less is generally better'. Get a program called autosort (or another called dirsort) as some programs need to be run in a certain order. This program allows you to change that order in one go.

I would definitely put NVDI in there for any desktop serious work - it does use a chunk of memory but is worth every byte, particularly if you want to run papyrus or Atari works.

If the SF354 are the drive belt models (which if they are single sided is highly likely),the belt has probably long since disintergrated. Would probably be worth opening them up and seeing if it has (you may find nothing but black gunk). In which case you may well have three faulty drives. If so they can be repaired easily with a new drive belt. As they have their own power supply they are unlikely to be effected if your STs is a bit weak, unless theirs is also on the way out. The internal drive on the STFM is more difficult to diagnose. On some models some capacitors fail stopping the drive from spinning, or if it is a real early drive (the very early STFMs did ship with single sided drives) then you may well have the same issue as the 354s. Or it might well be, as juansolo suggested, gunk on the floppy drive head. You can buy a floppy disk cleaning kit (or clean it yourself with a q-tip and some isopropyl. Another thing to note is that if the language disk is on a double sided disk, the 354s won't be able to read them as they are single sided only. Which may mean that only the STFM drive is caput.

With the floppy disks, I have actually found them to be a lot tougher than most people say.. provided they have been kept dry. A lot of so called 'dead' disks can be brought back to life if you gently clean them with isopropyl and a q-tip. Most of my floppies are still going strong in a 800 plus game collection and I still have a lot of random software disks that are also fine. They are all now stored in sealable plastic bags now to add to the protection. In my experience a properly cared for floppy disk will retain data for longer than a CD-R, which seem to spotaneously self destruct after about 10 years, regardless of how they are stored. I had one CDR turn to what appeared to be liquid inside itself, you could tip the CD and watch it run about.

In answer to your actual question though.. no it will not matter if you use a DSDD floppy, or even a DSHD one if you cover the HD select slot on the disk, though you won't be able to use HD disks at full capacity without more hardware mods, and they are allegedly less reliable formatted this way (not done this myself). I know there were 'single sided' floppies when the ST first came out, but they died out pretty quick. You can just format the DSDD disk as single sided if necessary. The best way to test the drives is to try and format a floppy. If it completes a format of both sides you are probably fine. If it only manages one side and none of the other then it is probably single sided. If it only partially formats either one, the heads need cleaning.